The closest to a nalgene-fitting billy is the ti-Lite, which is a lot larger than most of the cups, or a coffee can. I've been looking for a while for something in the .9 liter size for 1.0 liter nalgenes.
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-IronRaven

When a man dare not speak without malice for fear of giving insult, that is when truth starts to die. Truth is the truest freedom.